1. Field of the Invention
This invention relates to a titanium fiber or a titanium alloy fiber having an equivalent area diameter of 5-30 .mu.m and a method of producing the same, and more particularly to a titanium fiber or titanium alloy fiber having a large specific surface area and a method of producing the same.
Throughout the specification, the titanium and titanium alloy are generically called as "titanium".
2. Description of Related Art
Extrafine metal fibers having a diameter of about 5-30 .mu.m are used in various fields such as a material for a filter or a catalyst carrier, or as a filler for giving an electric conductivity or a strength to plastics, cloth and the like. As the extrafine metal fiber, there are widely used stainless fibers produced by a bundle-drawing method. On the other hand, it is demanded to develop a material for the filter or catalyst carrier having a corrosion resistance higher than that of the stainless fiber, or a filler having a light weight and a high strength as compared with those of the stainless fiber, and hence titanium fibers are recently noticed. Particularly, the titanium fibers having a larger specific surface area are demanded in the catalyst field requiring a surface area participant in the reaction as an important factor.
In the production of the extrafine metal fiber having a diameter of about 5-30 .mu.m, there is known a bundle-drawing method as follows.
For example, JP-A-2-52117 discloses a method wherein a bundle-drawn composite body (composite filament) having an outer housing of steel and containing metal fibers embedded in copper matrix is prepared, and then the outer housing of steel and the copper matrix (covering layer) are removed by substitution reaction and electrolysis to obtain a bundle of metal fibers. However, this method is not suitable for the production of titanium fibers having a large specific surface area because the titanium fiber obtained by this method is small in the surface unevenness, so that in order to obtain titanium fibers having a large specific surface area, the fiber size should be made finer and hence labor and cost required for the working undesirably increase.
And also, JP-A-5-177244 discloses a method wherein a covered wire consisting of a core wire of high corrosion-resistant alloy with a covering layer of steel having a carbon content of not more than 0.12% by weight is subjected to cold drawing to form a covered filament, and a plurality of the covered filaments are bundled and inserted into an inside of a steel tube to form a composite wire, and the composite wire is subjected to cold drawing to form a composite filament, and then the steel tube and portion corresponding to the coated layer are dissolved out by electrolysis to obtain a bundle of metal fibers. However, when this method is applied to the production of titanium fibers, it implies a problem of insufficient dissolution in the final step causing low yield of titanium fibers though the surface unevenness becomes can be made large as compared with the case of JP-A-2-52117.